A 3 ton Suburban with adapters from 8 lugs to a 5 lug pattern with 1/2" wheel studs..sounds like a scary huge downgrade to me !..

Even if it did work...I wouldn't!..
I'd sell the rims to finance the right ones to fit your truck..without adapters..
I have used wheel adapters only once on old air cooled VW's--they had two types available,one was cut from steel and the others were cast aluminum,with the studs made into the casting..
I used the steel ones on a '63 Beetle and a '63 VW Bus without any issues--the aluminum ones,one cracked when I had them on the rear of the bus with Chevy steel 15" rims and l-78-15 tires,I was going down a bumpy road with lots of potholes,hit one deep one and I heard a snap..
--then the bus started wobbling and I pulled right over--the tire leaned over towards the inner wheel well and got wedged in there,took me half an hour to jack it up and pry it out of there..good thing I had an original VW spare and a chevy one with me (as up front I wasn't using adapters),so I was able to limp home on the spare!..
I don't like the idea of wheel adapters on a truck,even a 1/2 ton..
When J.C. Whitney sold those,the ad stated in fine print "NOT for station wagons or trucks"..